Images acquired by medical imaging apparatuses (modalities) are used to inspect patients or examine affected regions thereof. Examples of such modalities used in the medical field include a simple X-ray imaging apparatus, an X-ray computed tomography (X-ray CT) imaging apparatus, a magnetic resonance imaging (MRI) apparatus, and an ultrasonic (US) imaging apparatus, among others.
By associating these images acquired by a plurality of different modalities, medical practitioners can examine a single region of a subject with a plurality of different types of images. For example, if an MRI tomographic image corresponding to an ultrasonic image captured by an ultrasonic imaging apparatus is acquired from a previously captured three-dimensional (3D) MRI image, doctors can give a diagnosis while comparing both images.
As a technique for realizing the above-described process, US2007/0010743 discusses acquiring the correspondence relationship between an ultrasonic image and an MRI image by setting the positional relationship between the reference object of a position sensor and a bed on which a patient lies and specifying a single predetermined point on a body surface with an ultrasonic probe having the position sensor. In this technique if the patient changes his/her direction or orientation on the bed, an error may be caused.